Thorium-magnesium alloys



A l i.

United States I ate 3,009,808 THORIUM-MAGNESIUM ALLOYS Cecil B. Griffith, Pierre V. Andreae, and Julian Glasser,

Chattanooga, Tenn., assignors, by direct and mesne assignments, of one-half to Republic Steel Corporation, Cleveland, Ohio, a corporation of New Jersey, and one-half to Vitro Corporation of America, a corporation of Delaware Filed Oct. 27, 1958, Ser. No. 769,684 8 Claims. (Cl. 75122.7)

This invention relates to magnesium base alloys, and more particularly to alloys of magnesium with thorium, and methods for preparing same.

Thorium is used as an alloying addition to magnesium for improving, among other properties, the magnesiums high temperature characteristics. It is diflicult to add thorium directly to molten magnesium, since the rate of solution is quite slow. Heretofore, the maximum thorium that could be added directly to molten magnesium was limited for practical use by the rate of solution.

While some of the significant magnesium alloys contain only 3% to 6% by weight of thorium, higher contents of thorium are desirable for master alloys, and in important structural magnesium alloys.

Often thorium-magnesium alloys contain undesirable impurities, for example, oxides. Elimination of contaminants is preferable for some products.

Accordingly, it is an object of the invention to provide method of manufacturing thorium-magnesium alloys of high thorium content, in which the alloys produced thereby may be used as master alloys, or as structural materials. It is another object of the invention to provide a process for preparing thorium-magnesium alloys' in which it is possible to obtain a high degree of purity and, especially, absence of oxides. Other objects of the invention will be apparent from a study of the ensuing description and appended claims.

Briefly stated, the present invention relates to method of preparing magnesium alloys with high thorium contents which comprises adding magnesium to a molten solution of a thorium halide in the presence of 'an a1kaline earth metal halide as a solvent or fluxing agent.

Referring to the drawing, there is shown liquidus curves for MgCl ThF and MgCl MgF systems. These curves are useful for selecting the amounts of materials to be employed in the reaction in order to obtain the lowest melting temperatures of the solution, as will be explained hereinafter.

The thorium halide may be thorium fluoride, thorium chloride,,thorium bromide, thorium iodide, or mixtures of the foregoing. It should be understood that the various thorium compounds will not be equally effective, and some will have greater efliciency in the reaction, and will be more practical in use, than others. Special preference is given to thorium fluoride and thorium chloride.

The molten salt solvent or fluxing agent may be an alkaline earth metal halide, for example, magnesium chloride, magnesium fluoride, magnesium bromide, calcium chloride, barium chloride, strontium chloride, and the like. Also, mixtures of the foregoing fluxing agents may be employed. Some fluxing agents are more eflicient and practical than others, and therefore the fluxing agents listed above should not be considered equally effective in the process of the invention. Preference is given to magnesium chloride, although it may be desirable to admix it with another salt.

Alkaline earth metal, as used herein, is defined as including magnesium, as well as calcium, barium, and strontium.

The reaction is usually carried out in a closed vessel 2 blanketed with an inert gas, for example, a noble gas, such as argon, or helium, in order to reduce the loss of thorium through oxidation. The materials used in the reaction should be dry, and preferably anhydrous. A convenient operation for producing dry materials is, for instance, to heat the solution of the thorium halide and the fluxing agent, for example, magnesium chloride, to dehydrating temperatures for a period of time suflicient to drive off the moisture. Even small quantities of moisture affect the reaction, and produce undesirable oxides.

Adequate mixing of the solution, as by stirring, is necessary during the reaction. Since the magnesium is lighter, and the alloy heavier, than the salts, contact between reactants may be lost, if mixing is not maintained until completion of the reaction.

For good separation, the alloy should contain enough thorium to be heavier than the salts, usually approximately at least 20% by weight thorium.

The amount of alkaline earth metal halide fluxing agent present preferably should be suflicient to form a low melting solution with both the thorium halide, and the magnesium halide formed by the reaction. Referring to the system shown in the drawing, if it is assumed that the maximum magnesium fluoride desired to be formed as a lay-product salt is 25% by weight, this would limit the thorium fluoride inthe starting material to about 45% by weight which is also low enough to give alow melting mixture. Thus, in that system, in order .to obtain the lower melting points of the solutions prior to and after the reaction, thorium fluoride should be present in amounts broadly in the range from about 10% to about by weight, preferably from about 15% to about 40% by weight.

As specific examples of magnesium base alloys and methods for preparing the same the following are given, it being understood, however, that these are only illustrative and are not intended in any way to limit the invention as to the materials employed or the proportions thereof.

EXAMPLE I A mixture of 200 gms. of magnesium chloride and 100 gms. of thorium fluoride were added to a reactor ves sel, dried at about 200 C., melted under argon gas, and stirred with an argon bubbler. Magnesium (250 gms.) was then added to the molten salt mixture as a one-half inch rod while stirring the reaction mass continuously with argon. After the reaction, the argon bubbler was withdrawn to allow separation of the metal and the salt. The furnace was held at temperatures for two hours he fore cooling. The reactor was then removed from the furnace and cut with a pipe cutter to permit removal of the contents. The amount of thorium contained in the magnesium alloys as determined by ananalysis was 18% by weight.

EXAMPLE II An attempt was made to form a reaction without the use of a magnesium chloride flux. In this experiment 89 EXAMPLE III This experiment was conducted using the same comit is free of salt and oxidecontaminants.

EXAMPLE IV This experiment was similar to Example III above in that care was taken to obtain dry study materials. Also enough magnesium was added to make an'alloy containing 42% by weight of thorium, the eutectic composition.

described, provided the features stated in any of the claims or equivalent thereof be employed.

We, therefore, particularly point out and claim as the invention: I

1. In a method for preparing magnesium alloys contain- I ing at least about 20% by Weight ofthorium, the steps which.comprise forming a melt of thorium halide and alkaline earth metal halide in which the amount of thorium halide ranges from about to about 60% by weight of said melt, and subjecting said melt to the reducing action of molten magnesium in amounts sutiicient for the resultant alloy to contain at least 20% by Weight of thorium.

On removal from the reactor of the contents were separated into three layers:

(a) Avery light metallic ingot on top, apparently pure magnesium; a

(b) A middle layer of salt; and

(c) A bottom layer of a heavy metallic substance.

The heavy metallic substance when analyzed contained 57.1% by Weight or thorium.

Other data obtained in the above examples are set forth in thefollowing table:

melt, and subjecting said melt to the reducing action of 25.

2. The method of claim 1 wherein said thorium halide is thorium fluoride and said alkaline earthmetal halide is magnesium chloride.

, 3. The method of claim 1 wherein said thoriumihalide is thorium chloride.

4. In a method for preparing magnesium alloys contain- 1 ing at least 20% by weight of thorium, the steps which comprise forming a melt of thorium halide and alkaline earth metal halide in whichthe amount of thorium halide ranges from about 1 0% to about 60% by weight of said molten magnesium in amounts sufiicient to forma magnesium alloy of suflicient density to sink below said melt under the atmosphere of a noble gas, so that the thorium is alloyed with magnesium- Table I TABULAIION OF THORIUM-MAGNESIUM ALLOY EXAMPLES Wt. Percent Th Wt. Thorium Wt. Wt. Metal -Recov- Thorium Fein Example No. 'Ihm, Mg, Rccovered, in Salt, Alloy gm. gm. Theo- Experiered Percent Percent retical mental 1 I 100 250 24. 4 18 282 68 5.4 0. 22%. a II. 89 226 23. 9 18 220 59 0. 11 III -Q 102 174 32. 4 24 240 78 0. 1 0. 18-1. 7 (Remelt of Examples I, II

and III) 21. 3 18 500 85 0. 11-4. 2

Upper ingot 100 120 41. 8 0.0 85 0 2. 5 0.01 Lower ingot i 57.1 95 72. 5 1.13

1 Percent thorium in alloy approximate since ingot was not completely homogeneous.

9 Not determined.

magnesiumstructural alloy. Thus, the high thorium con- 5. In a method for preparing magnesium alloys con- 7 taining at least 20% by weight of thorium, the steps which comprise forming a melt o-f thoriumv halide and alkaline. earth metal halidein which the amountfof thorium halide ranges from about 10% to about 60% by weight of said melt, and subjecting said melt to the reducing'action of molten magnesium in sufli'cient amounts to form a magnesium alloy of sufiicientdensity to sink below the melt. 6. The method of claim 5 wherein said thorium halide is thorium-fluoride and said alkaline. earth metal halide is a magnesium halide. V

7. The method of claim 6 wherein said halide is magnesium chloride. I p '8. The method of claim 5 wherein saidthorium halide is thorium chloride. l

I References Cited in the file ot this, patent UNITED STATES PATENTS 2,678,267 Saunders May 11, 1954 magnesium 

1. IN A METHOD FOR PREPARING MAGNESIUM ALLOYS CONTAINING AT LEAST ABOUT 20% BY WEIGHT OF THORIUM, THE STEPS WHICH COMPRISE FORMING A MELT OF THORIUM HALIDE AND ALKALINE EARTH METAL HALIDE IN WHICH THE AMOUNT OF THORIUM HALIDE RANGES FROM ABOUT 10% TO ABOUT 60% BY WEIGHT OF SAID MELT, AND SUBJECTING SAID MELT TO THE REDUCING ACTION OF MOLTEN MAGNESIUM IN AMOUNTS SUFFICIENT FOR THE RESULTANT ALLOY TO CONTAIN AT LEAST 20% BY WEIGHT OF THORIUM. 